1. Field of the Invention:
This invention relates to electronic still cameras having a solid state image pickup element comprised of a plurality of photosensitive elements capable of field readout or frame readout and arranged adjacent to each other.
2. Description of the Related Art:
FIG. 1 is a diagram illustrating the circuit structure of an inter-line transfer CCD 1 which is used in the conventional electronic still camera. In the FIG., 13, 14 are respective photo-diodes for converting photo-signals to electric charges. 15 is a vertical transfer CCD (hereinafter referred to as V-CCD) for transferring the electric charges vertically. 16 is a horizontal transfer CCD (hereinafter referred to as H-CCD) for reading out the electric charges horizontally. The electrical charges are converted to voltages by an output amplifier 17. Also, 18 is terminals at which vertical transfer pulses of four phases for driving the V-CCD 15 enter. 19 are a terminal at which a horizontal transfer pulse for driving the H-CCD 16 enters. Upper and lower drains 20 and 21 for clearing the electric charges include gates for selectively clearing the electric charges.
In FIG. 1, of the input terminals 18 for the vertical transfer pulses, the terminals .phi..sub.V1 and .phi..sub.V3 also serve as transfer gate electrodes from the photo-diodes 13 and 14 to the V-CCD 15, and are driven by pulses of such three values as shown in FIG. 2. That is, when the pulses .phi..sub.V1 and .phi..sub.V3 become +V, the gates open and electric charges transfer from the photo-diodes 13 and 14 to those electrodes in the V-CCD 15 to which the pulses .phi..sub.V1 and .phi..sub.V3 are applied. After that, the usual 4-phase drive pulses .phi..sub.V1 -.phi..sub.V4 each are applied between 0 and -V shown in FIG. 2 to perform vertical transfer of the electric charges.
In such a conventional device as has been described above, when reading a frame, the time from the clearing to the reading of each photosensitive element differs between the adjacent upper and lower photosensitive elements each, by which difference is produced in the amount of dark current stored in each and the degree of unevenness. Therefore, there was a problem in that a flicker phenomenon and an unnatural image were produced.